Gas automatic detection alarm circuit

The gas alarm circuit takes advantage of the fact that the specific gravity of OC gas is greater than
that of ordinary air, and uses a pressure sensitive element to convert the pressure difference into an electrical signal. After the
signal is amplified, it drives the actuator and sends out an alarm signal.
    Figure 13-26 is the circuit diagram of the gas alarm device. During operation,
the 220V mains power is first stepped down by the capacitor G to limit the current, and then
rectified by a bridge rectifier connected by 2CP18×4, and stabilized by vs and filtered by 6;
low-voltage direct current is provided to the circuit. Ri, R2, Hurricane and Hurricane form a bridge
, and its output is connected to the input end of the differential amplifier composed of VT1 and VT2
. The amplified DC signal drives VT3 to activate relay K
and turn on the alarm circuit.
    In the figure, R4 is a force-sensitive resistor, and a semiconductor strain gauge can be used as Ra. R3 is a resistor with the same resistance value as R4. In order to eliminate the temperature effect
tR, it can be replaced by the same force-sensitive resistor as the product, but R3 should be sealed in a high-strength container so that it is only affected by temperature and not by air pressure
. ,
    VT1 and VT2 are required to be used in pairs, and the multiples of VI and 3 should be larger. The relay can be selected as RJX-4 type.
    When adjusting, first determine R and R, and then determine the resistance values ​​of R: and R2 based on the resistance values ​​of R3 and R4. Let Rl -Rz, its resistance is R. Or
1/2~1/3 of the product. Potentiometer RP is used to zero the differential amplifier.
    1. Alarm circuit , after assembly. It is best to place it on the indoor floor near the corner. The trapped gas is relatively heavy and will always
fall to low places along the wall indoors .